A hydraulic valve directs the flow of a liquid medium, usually oil, through a hydraulic system. The direction of the oil flow is determined by the position of a spool or a poppet. An example valve may have a movable element inside a housing or sleeve. For instance, the valve may include a poppet that is movable by an actuation mechanism (e.g., electric, hydraulic, pneumatic, or manual). The poppet may be seated on a valve seat formed inside the housing. Once the valve is actuated, the poppet moves off the seat to allow flow around the poppet from a first port to a second port. In another example, the valve may be normally-open, and when the valve is actuated, the poppet is seated to block flow through the valve.
In examples, if the valve is a manually-actuated valve, then to actuate the valve, an operator may apply a large force to overcome a large spring force applied by a spring having a high spring rate and cause the poppet to be move. If the valve is electrically-actuated, e.g., via a solenoid, in some cases, the solenoid fails and it may be desirable to have a manual override feature to allow the valve to be manually activated to place a machine in a safe condition. Using the manual override feature could also involve applying the large force that overcomes the aforementioned large spring force.
Further, in some examples, it may be desirable to include a detent mechanism in the valve such that when the valve is actuated the detent mechanism is engaged to keep the movable element locked in place. In the case of a large spring force, the detent mechanism is configured to be able to oppose the large spring force, and as such the detent mechanism may be complicated and costly.
Therefore, it may be desirable to have a valve that has a manual actuation mechanism that enables using a soft spring having a small spring rate such that the manual actuation force is reduced and the complexity and cost of an associated detent mechanism is also reduced.